1. Field of the Invention
There are many uses for fluorescent compounds or conjugates. Fluorescent compounds may be used as fluorescent labels for cell sorters, diagnostic assays, histology, fluorescence microscopy, immunocytochemical localization of antigenic markers, particularly for pathogens, and the like. The particular fluorescent label employed plays an important part in the sensitivity and accuracy of any particular methodology. In many situations, the sample which is involved has endogenous fluorescence which can provide for a substantial background. Other errors can be introduced through Rayleigh and Raman scattering. Many of these problems can be substantially alleviated, if not avoided, by having large Stokes shifts and emission at long wavelengths. The excitation light which is employed is at substantially shorter wavelengths from the emission light, so that the background light may be filtered out. It is therefore desirable to provide fluorescent labels which not only have high quantum efficiencies, so as to provide for intense signals, but also avoid the background error resulting from background fluorescence.
2. Description of the Prior Art
Properties of phycobiliproteins are described by Oi et al., J. Cell Biol. (1982) 93:981-986. Characteristics of phycobiliproteins may be found in Glazer and Hixson, J. Biol. Chem. (1977) 252:32-42 and Grabowski and Gantt, Photochem. Photobiol. (1978) 28:39-45. See also Lundell and Glazer, J. Biol. Chem. (1981) 256:12600-12606. Other references of interest are Glazer, 1981, in The Biochemistry of Plants, Hatch and Boardman, eds., Academic Press, New York 8:51-96, Bryant et al., Arch. Microbiol. (1976) 110:61-75 and Stryer, Ann. Rev. Biochem. (1978) 47:819-846. See particularly, Sigman et al., "The Evolution of Protein Structure and Function," 1980, Academic Press, N.Y., Glazer, In Structure and evolution of photosynthetic accessory pigment systems with special reference to phycobiliproteins, pp. 221-144.